The Coordination Behavior of Oxygen‐depleted Calixarenes towards d 10 Noble Metal Ions

A calix[4]arene, in which two of the phenol functions are replaced by pyrazole units, [H 2 (bpzCal)], was investigated as a ligand for Cu + , Ag + and Au + ions. Using [Cu(MeCN) 4 ]BF 4 and AgSbF 6 as the precursors, complexes [MH 2 (bpzCal)]X (M = Cu, X = BF 4; M = Ag, X = SbF 6 ) were formed, where the calixarene ligands adopt a 1,3‐alternate structure and the metal ions are coordinated linearly by the two pyrazolyl donors. [CuH 2 (bpzCal)]BF 4 displayed a – for copper(I) complexes – unusual stability towards O 2 , which is due to the steric protection of the Cu I center. By contrast a dinuclear copper(I) complex [Cu 2 (bpzCal)] that was obtained through treatment of [H 2 (bpzCal)] with two equivalents of Cu(HMDS) is rather sensitive towards O 2 . The preparation of a gold complex required the employment of a gold precursor, which contains one labile and one stabilizing neutral ligand, namely [(PPh 3 )Au(NCMe)]SbF 6 , which led to the formation of [(PPh 3 )AuH 2 (bpzCal)]SbF 6 . In this complex [H 2 (bpzCal)] acts only as a monodentate ligand for the gold center. Taken together, the results demonstrate the potential of [H 2 (bpzCal)] in providing rather different coordination spheres for metal ions.